JP2015031720A - Transfer unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend the service life of a cleaning member and a transfer belt, while maintaining cleaning effect of the cleaning member which cleans a rear surface of the transfer belt.SOLUTION: An intermediate transfer unit 50 includes: an intermediate transfer belt 125; primary transfer rollers 126 for each color; a drive mechanism 52 for bringing the color-image-forming primary transfer rollers 126 close to/away from the intermediate transfer belt 125; a cleaning member 531 for cleaning a rear surface of the intermediate transfer belt 125; and a moving mechanism 530 for moving the cleaning member 531 to a position in contact with the rear surface when the drive mechanism 52 moves the color-image-forming primary transfer rollers 126 to the position in contact with the intermediate transfer belt 125, and moving the cleaning member 531 to a position separated from the rear surface when the drive mechanism 52 moves the color-image-forming primary transfer rollers 126 to the position separated from the intermediate transfer belt 125.

Description

  The present invention relates to a transfer unit and an image forming apparatus, and more particularly to a mechanism for cleaning a transfer belt.

  In an image forming apparatus, a toner image formed on the peripheral surface of each color photoconductor drum (image carrier) for color image formation is temporarily transferred to an endless transfer belt, and the respective color toner images are superimposed. It is known that a color toner image is formed, and the toner image is secondarily transferred to a recording medium to form an image. There is also known an image forming apparatus that transfers a toner image directly from a photosensitive drum to a recording medium conveyed by the transfer belt.

  In such an image forming apparatus, when toner is transferred from the photosensitive drum, toner scattering occurs, the inside of the apparatus is contaminated, and the transfer belt may become dirty to the back surface. For this reason, as shown in Patent Document 1 below, a mechanism for cleaning the back surface of the transfer belt in order to prevent deterioration in image quality due to unstable running of the intermediate belt caused by scattering toner or foreign matter adhering to the back surface of the transfer belt Has also been proposed.

JP 2009-31450 A

  However, the cleaning mechanism disclosed in Patent Document 1 keeps the cleaning member in constant contact with the back surface of the transfer belt and cleans the back surface by friction between the cleaning member and the back surface of the transfer belt. There is a problem that the life of the member and the transfer belt is shortened.

  SUMMARY An advantage of some aspects of the invention is that it extends the life of a cleaning member and a transfer belt while maintaining the cleaning effect of a cleaning member that cleans the back surface of the transfer belt.

  A transfer unit according to one aspect of the present invention runs while being stretched between a plurality of rollers, and a toner image formed by an image carrier of each color necessary for color and monochrome image formation is transferred to the surface or A transfer belt that is transferred to a recording medium placed on the surface, a transfer roller that is provided for each image carrier, applies a transfer potential to the transfer belt, and transfers the toner image to the transfer belt; Of the transfer rollers for color and monochrome image formation, a drive mechanism for contacting and separating the transfer rollers for color image formation with respect to the transfer belt, and the back surface of the transfer belt can be contacted. A cleaning member that cleans the cleaning roller, and the drive mechanism moves the transfer rollers for forming the color image to a position in contact with the transfer belt. When the member is moved to a position in contact with the back surface of the transfer belt, and the drive mechanism moves the transfer rollers for forming the color image to positions away from the transfer belt, the cleaning member is moved to the transfer belt. And a moving mechanism for moving the belt to a position away from the back surface of the belt.

  In the present invention, when each transfer roller for color image formation is moved to a position where it contacts the transfer belt, the cleaning member moves to a position where it contacts the back surface of the transfer belt, and each transfer roller for color image formation moves. Since the cleaning member moves to a position away from the back surface of the transfer belt when moved to a position away from the transfer belt, the cleaning of the back surface of the transfer belt by the cleaning member is performed only during color image formation. Since the back surface of the transfer belt has a smaller amount of toner adhesion than the surface of the transfer belt and does not need to be kept in constant contact with the surface of the transfer belt, there is no need to keep the cleaning member in contact with the back surface of the transfer belt. By separating the cleaning member from the back surface of the transfer belt, the cleaning member and the transfer belt can be released from friction while maintaining the cleaning effect of the cleaning member, and the life of both members can be extended.

  According to the present invention, it is possible to extend the life of the cleaning member and the transfer belt while maintaining the cleaning effect of the cleaning member for cleaning the back surface of the transfer belt.

1 is a front sectional view showing a structure of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a perspective view illustrating a schematic configuration in a casing of an intermediate transfer unit. FIG. 3 is a perspective view illustrating a state in which an external appearance of an intermediate transfer unit is viewed from below in FIG. 2. FIG. 4 is a plan view showing a state in which the intermediate transfer unit is viewed from below in FIG. 3, and shows a schematic configuration of the intermediate transfer unit. FIG. 4 is a side view of the intermediate transfer unit, and shows a portion where the drive mechanism and the cleaning unit are locked. FIG. 6 is a side view showing a state in which the first support member is moved to a position where the driving mechanism separates each primary transfer roller for forming a color image from the intermediate transfer belt.

  Hereinafter, a transfer unit according to an embodiment of the present disclosure and an image forming apparatus including the transfer unit will be described with reference to the drawings. FIG. 1 is a front sectional view showing the structure of an image forming apparatus having a developing device according to an embodiment of the present invention.

  The image forming apparatus 1 according to an embodiment of the present disclosure is a multifunction machine having a plurality of functions such as a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus 1 includes an apparatus main body 11 that includes an operation unit 47, an image forming unit 12, a fixing unit 13, a paper feeding unit 14, a document feeding unit 6, a document reading unit 5, and the like.

  When the image forming apparatus 1 performs a document reading operation, the document reading unit 5 optically reads a document fed by the document feeding unit 6 or a document placed on the document placing glass 161, Generate image data. Image data generated by the document reading unit 5 is stored in a built-in HDD or a network-connected computer.

  When the image forming apparatus 1 performs an image forming operation, the image forming unit 12 is supplied from the paper supply unit 14 based on the image data generated by the document reading operation or the image data stored in the built-in HDD. A toner image is formed on a recording paper P as a recording medium to be paper. The image forming units 12M, 12C, 12Y, and 12Bk of the image forming unit 12 include a photosensitive drum 121, a charging device 123, an exposure device 124, a developing device 122, and a primary transfer roller 126, respectively. .

  Each developing device 122 of the image forming units 12M, 12C, 12Y, and 12Bk contains toner for developing an electrostatic latent image. The developing device 122 supplies the toner to the surface of the photosensitive drum 121 that has been charged by the charging device 123 and exposed by the exposure device 124.

  When performing color printing, the magenta image forming unit 12M, the cyan image forming unit 12C, the yellow image forming unit 12Y, and the black image forming unit 12Bk of the image forming unit 12 each receive image data. A toner image is formed on the photosensitive drum 121 by charging, exposure, and development processes based on the image composed of each color component, and the toner image is driven by the primary transfer roller 126 by the driving roller 125a and the driven roller 125b. The image is transferred onto an intermediate transfer belt (transfer belt) 125 that is stretched around the belt.

  The intermediate transfer belt 125, the primary transfer roller 126, the driving roller 125a, and the driven roller 125b are mounted on the intermediate transfer unit 50.

  The intermediate transfer belt 125 is driven by a driving roller 125 a in a state where an image carrying surface on which a toner image is transferred is set on the outer peripheral surface thereof and in contact with the peripheral surface of the photosensitive drum 121. The intermediate transfer belt 125 travels endlessly between the driving roller 125a and the driven roller 125b while being synchronized with each photosensitive drum 121.

  The toner images of the respective colors transferred onto the intermediate transfer belt 125 are superimposed on the intermediate transfer belt 125 with the transfer timing adjusted to become a color toner image. The secondary transfer roller 210 conveys the color toner image formed on the surface of the intermediate transfer belt 125 from the sheet feeding unit 14 through the conveyance path 190 at the nip N between the intermediate transfer belt 125 and the driving roller 125a. The recording sheet P is transferred. Thereafter, the fixing unit 13 fixes the toner image on the recording paper P to the recording paper P by thermocompression bonding. The recording paper P on which the color image has been formed after completion of the fixing process is discharged to a discharge tray 151.

  Next, the intermediate transfer unit 50 will be described. FIG. 2 is a perspective view showing a schematic configuration in the casing of the intermediate transfer unit 50. FIG. 3 is a perspective view showing the appearance of the intermediate transfer unit 50 as viewed from below in FIG. FIG. 3 shows a state where the intermediate transfer belt 125 is removed.

  As described above, the intermediate transfer unit 50 includes the intermediate transfer belt 125, the primary transfer roller 126, the driving roller 125a, and the driven roller 125b. The intermediate transfer unit 50 is an embodiment of the transfer unit in the claims.

  The image forming units 12Bk, 12M, 12C, and 12Y other than the primary transfer roller 126 are disposed below the intermediate transfer unit 50 in FIG.

  The frame 51 supports each mechanism provided in the intermediate transfer unit 50. The frame 51 includes a primary transfer roller 126, a driving roller 125a, and a driven roller 125b, two backup rollers 129, a primary transfer roller 126 of the black image forming unit 12Bk, a cleaning unit 53, and a drive. A mechanism 52 is attached.

  The backup roller 129 presses the intermediate transfer belt 125 from the inside of the intermediate transfer belt 125 stretched between the driving roller 125 a and the driven roller 125 b to apply tension to the intermediate transfer belt 125.

  The driving mechanism 52 is a primary transfer roller 126 for forming a color image among the photosensitive drums (image carriers) 121 for forming color and monochrome images, that is, an image forming unit 12M for magenta, and a cyan image forming unit. The primary transfer rollers 126 of the image forming unit 12C and the yellow image forming unit 12Y are supported. The drive mechanism 52 is a mechanism for bringing the primary transfer rollers 126 for color image formation into contact with and separating from the intermediate transfer belt 125.

  The drive mechanism 52 includes a first rotation shaft 521, a first support member 522, and a rotation drive unit 524 (FIG. 5).

  The first rotating shaft 521 extends in the rotating shaft direction of the driving roller 125a and the driven roller 125b. The first rotation shaft 521 serves as a fulcrum for rotating the first support member 522 in the contact / separation direction with respect to the frame 51 and the intermediate transfer belt 125.

  The first support member 522 rotatably supports the primary transfer rollers 126 for forming color images arranged in the running direction of the intermediate transfer belt 125. The first support member 522 rotates with the first rotation shaft 521 as a fulcrum. By this rotation, the first support member 522 rotates and moves the primary transfer rollers 126 for color image formation in a direction in which they are in contact with and separated from the back surface of the intermediate transfer belt 125.

  The rotation drive unit 524 includes a drive source that supplies a rotation drive force, a rotation shaft that rotates by the rotation drive force from the drive source, a cam that has a different diameter at each circumferential surface position, and that rotates with the rotation shaft, 1 includes a pressing portion (not shown) including a pressing spring that presses the support member 522 in a direction away from the back surface of the intermediate transfer belt 125 and the frame 51, and a control unit that drives and controls the driving source. . The cam is attached to the intermediate transfer unit 50 with its peripheral surface in contact with the first support member 522, and the cam is rotated toward the back surface of the intermediate transfer belt 125 and the frame 51 against the pressing by the pressing portion. By varying the amount by which the first support member 522 is pushed in, the first support member 522 rotates and moves in a direction in which the first support member 522 contacts and separates from the back surface of the intermediate transfer belt 125 according to the rotation of the cam. The contact / separation state of the first support member 522 with respect to the back surface of the intermediate transfer belt 125 is switched due to the difference in diameter between the peripheral surfaces of the cam.

  When forming a color image, the control unit drives and controls the drive source to rotate the cam, and the distance from the rotation center of the cam to the peripheral surface (first support member 522) is, for example, the maximum. Stop cam rotation. In this state, the pressing amount of the first support member 522 toward the back surface of the intermediate transfer belt 125 is, for example, the maximum, and the positions at which all the primary transfer rollers 126 of each color for color image formation are in contact with the back surface of the intermediate transfer belt 125. The first support member 522 is set so as to be moved.

  In addition, when the monochrome image is formed, the control unit drives and controls the drive source to rotate the cam, and stops the rotation of the cam at a position where the distance from the rotation center of the cam to the peripheral surface becomes the minimum, for example. In this state, the pressing amount of the first support member 522 toward the back surface of the intermediate transfer belt 125 is, for example, the minimum, and all the primary transfer rollers 126 of each color for color image formation are at positions away from the back surface of the intermediate transfer belt 125. The first support member 522 is set to rotate.

  The cleaning unit 53 is a mechanism for cleaning the back surface (inner surface) of the intermediate transfer belt 125. The cleaning unit 53 includes a cleaning member 531 (FIG. 4) and a moving mechanism 530 (FIG. 4). Details of the cleaning unit 53 will be described later.

  A driving roller 125a is rotatably supported at one end of the frame 51, and a driven roller 125b is supported at the other end. The intermediate transfer belt 125 is stretched between the driving roller 125a and the driven roller 125b supported in this manner, and travels in the rotation direction as the driving roller 125a rotates. All the primary transfer rollers 126 are disposed inside the intermediate transfer belt 125 in a stretched state.

  Next, the configuration of the drive mechanism 52 and the cleaning unit 53 will be further described. 4 is a plan view showing a state in which the intermediate transfer unit 50 is viewed from below in FIG. 3, and shows a schematic configuration of the intermediate transfer unit 50. FIG. FIG. 5 is a side view of the intermediate transfer unit 50 and shows a portion where the drive mechanism 52 and the cleaning unit 53 are locked.

  First, the configuration of the cleaning unit 53 will be described. The cleaning unit 53 includes a cleaning member 531 and a moving mechanism 530.

  The cleaning member 531 extends in the rotation axis direction of the driving roller 125a and the driven roller 125b, and has a length close to the width of the intermediate transfer belt 125 (a dimension in a direction orthogonal to the traveling direction). The cleaning member 531 can be brought into contact with the back surface of the intermediate transfer belt 125, and scrapes and cleans (brushes) waste toner, dust, and the like adhering to the back surface due to friction with the back surface during the contact. The cleaning member 531 is formed of a conductive material.

  The moving mechanism 530 is a rotating mechanism that rotates the cleaning member 531 in a direction in which the cleaning member 531 comes in contact with and separates from the back surface of the intermediate transfer belt 125. The moving mechanism 530 includes a second rotating shaft 532 and a second support member 533.

  The second rotating shaft 532 extends in the rotating shaft direction of the driving roller 125a and the driven roller 125b. The second rotation shaft 532 serves as a fulcrum for rotating the second support member 533 in the contact / separation direction with respect to the frame 51 and the intermediate transfer belt 125.

  Similarly to the cleaning member 531, the second support member 533 extends in the rotation axis direction and supports the cleaning member 531. The second support member 533 is attached to the surface of the cleaning member 531 that is opposite to the surface facing the back surface of the intermediate transfer belt 125. The second support member 533 rotates in the arrow A direction about the second rotation shaft 532 while supporting the cleaning member 531. Accordingly, the second support member 533 rotates the cleaning member 531 in a direction in which the cleaning member 531 comes in contact with and separates from the back surface of the intermediate transfer belt 125. In the traveling direction of the intermediate transfer belt 125, the cleaning unit 53 is opposite to the first support member 522 side on which the primary transfer rollers 126 for color image formation are disposed with respect to the first rotation shaft 521. It is arranged at the position.

  Next, the configuration of the locking mechanism for the drive mechanism 52 and the cleaning unit 53 will be described.

  An engagement portion 525 that engages with the first rotation shaft 521 is formed on the first support member 522 of the drive mechanism 52. The engaging portion 525 includes a first engaging portion 525a and a second engaging portion 525b. The first engagement portion 525a engages with one side portion of the first rotation shaft 521. The second engagement portion 525b engages with the other one side portion of the first rotation shaft 521. With the first engagement portion 525a and the second engagement portion 525b, the engagement portion 525 includes the first rotation shaft 521, so that the first support member 522 can rotate in the direction of the arrow B to perform the first rotation. It is supported by the shaft 521.

  Further, the second support member 533 of the moving mechanism 530 is engaged with the end portion of the second engagement portion 525b at the end portion opposite to the side supporting the cleaning member 531 with respect to the second rotation shaft 532. The 2nd latching | locking part 533a which stops is provided.

  The second locking portion 533a has a recess 5331. The concave portion 5331 is formed in such a size that the end portion of the second engaging portion 525b can be fitted therein. The first support member 522 is locked to the second support member 533 by the end portion of the second engagement portion 525b being inserted into the recess 5331 as the first locking portion 522a.

  As described above, the first support member 522 that supports each primary transfer roller 126 for color image formation is pressed by the pressing portion so as to rotate and move away from the back surface of the intermediate transfer belt 125. . In contrast, the second support member 533 that supports the cleaning member 531 is pressed by a pressing member (not shown) so that the cleaning member 531 rotates in a direction approaching the back surface of the intermediate transfer belt 125.

  The frame 51 is provided with a shaft support 516 of the black primary transfer roller 126. The first support member 522 is provided with a shaft support portion 517 of the primary transfer roller 126 for each color for color image formation. 5 and FIG. 6 to be described later show a shaft support 517 of the primary transfer roller 126 for yellow.

  FIG. 6 is a side view showing a state in which the first support member 522 is moved to a position where the driving mechanism 52 separates each primary transfer roller 126 for color image formation from the intermediate transfer belt 125. The operation of the driving mechanism 52 and the moving mechanism 530 will be described with reference to FIG. 6 and FIG.

  In FIG. 5, the drive mechanism 52 rotates and moves the first support member 522 to the position where each primary transfer roller 126 for color image formation contacts the back surface of the intermediate transfer belt 125 by the above-described cam rotation control. The first support member 522 in a state where the cleaning member 531 is in contact with the back surface of the intermediate transfer belt 125 is shown.

  At this time, the second support member 533 that supports the cleaning member 531 is pressed by the pressing member so that the cleaning member 531 rotates in the direction approaching the back surface of the intermediate transfer belt 125 (the −Y direction in FIG. 5). Therefore, the second locking portion 533a is urged in the direction of rotation toward the + Y direction in FIG. 5 with the second rotation shaft 532 as a fulcrum.

  However, in this state, the first locking portion 522a of the first support member 522 on the drive mechanism 52 side enters the recessed portion 5331 of the second locking portion 533a. The first support member 522 is pressed to the + Y direction side (the direction side away from the back surface of the intermediate transfer belt 125) by the pressing portion described above, but is stably in a state where the rotation by the pressing is stopped by the cam. It has stopped. For this reason, the force which the 2nd latching | locking part 533a tries to rotate toward the + Y direction side is stopped by latching with the 1st latching | locking part 522a.

  Thereby, the 2nd support member 533 stops in the state which the 2nd latching | locking part 533a latched with the 1st latching | locking part 522a, and is maintained in this state. In this embodiment, when the second support member 533 is stopped in this state, the posture of the second support member 533 is set so that the upper surface of the cleaning unit 531 is in contact with the back surface of the intermediate transfer belt 125. Has been.

  On the other hand, the drive mechanism 52 controls the rotation of the cam as described above, and as shown in FIG. 6, the first support member 522 is moved to a position where each primary transfer roller 126 for color image formation is separated from the back surface of the intermediate transfer belt 125. Is rotated in the + Y direction side, the first locking portion 522a of the first support member 522 is rotated on the first rotation shaft 521 as a fulcrum, so that the −Y direction side from the state shown in FIG. Move to.

  By the movement of the first locking portion 522a toward the −Y direction side, the first locking portion 522a presses the locked second locking portion 533a so as to rotate toward the −Y direction side. To do. The pressing force of the second locking portion 533a by the first locking portion 522a is the pressing force applied to the second support member 533 by the pressing member (the direction in which the cleaning member 531 approaches the back surface of the intermediate transfer belt 125 ( It is set to be larger than the pressing force (rotating the second support member 533 in the -Y direction in FIG. 5). Therefore, when the first locking portion 522a is pressed against the second locking portion 533a, the cleaning member 531 side of the second support member 533 is on the + Y direction side (the intermediate transfer belt 125 of the intermediate transfer belt 125) with the second rotation shaft 532 as a fulcrum. Rotate towards the side away from the back. Here, when the first support member 522 is moved to a position where each primary transfer roller 126 for color image formation is moved away from the back surface of the intermediate transfer belt 125, the second locking by the first locking portion 522a. The rotation amounts of the first support member 522 and the second support member 533 are set so that the cleaning member 531 is separated from the back surface of the intermediate transfer belt 125 by the pressing of the portion 533a.

  That is, in the present embodiment, the first support member 522 is driven closer to the moving mechanism 530 than the first rotation shaft 521 and the second support member 533 is driven more than the second rotation shaft 532. The second locking portion 533a provided on the mechanism 52 side is locked. When the first support member 522 rotates the primary transfer rollers 126 for color image formation in a direction away from the back surface of the intermediate transfer belt 125 by the rotation driving unit 524, the first locking unit 522a is in the second relationship. The stopper 533a is pressed to rotate the second support member 533 in the direction in which the cleaning member 531 is separated from the back surface, with the second rotation shaft 532 as a fulcrum.

  With this configuration, the moving mechanism 530 causes the cleaning member 531 to move to the back surface of the intermediate transfer belt 125 when the drive mechanism 52 moves the primary transfer rollers 126 for color image formation to positions where they contact the intermediate transfer belt 125. When the driving mechanism 52 moves each primary transfer roller 126 for color image formation to a position away from the intermediate transfer belt 125, the cleaning member 531 is moved from the back surface of the intermediate transfer belt 125. It will move to the position which leaves | separates.

  Thus, in the present embodiment, the cleaning of the back surface of the intermediate transfer belt 125 by the cleaning member 531 is performed only at the time of color image formation. The back surface of the intermediate transfer belt 125 has a smaller amount of toner adhesion than the front surface of the intermediate transfer belt 125 (the surface on which the toner image is transferred from the photosensitive drum 121), and does not need to be constantly contacted and cleaned. As described above, the cleaning member 531 is kept in contact with the back surface of the intermediate transfer belt 125, and the cleaning member 531 is separated from the back surface of the intermediate transfer belt 125 for a certain period of time, thereby maintaining the cleaning effect of the cleaning member 531. However, the cleaning member 531 and the intermediate transfer belt 125 can be released from friction, and the lifetime of both can be extended.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above embodiment, the cleaning member 531 is rotated by the second support member 533 and contacts the back surface of the intermediate transfer belt 125 during color image formation, but the cleaning member 531 contacts the back surface of the intermediate transfer belt 125. Sometimes, the cleaning member 531 presses the intermediate transfer belt 125 stretched between the driving roller 125a and the driven roller 125b from the inner side (back surface) to the outer side, so that the intermediate transfer belt 125 projects outward. In addition, the postures and positions of the second support member 533 and the cleaning member 531 during the color image formation may be set. This makes it possible to cause the cleaning member 531 to perform the same operation as the backup roller during color image formation.

  In the above embodiment, the intermediate transfer unit 50 configured to transfer the toner image from the photosensitive drum 121 onto the intermediate transfer belt 125 is described. However, the present invention is not limited to this, and the transfer is not limited thereto. A transfer unit in which the belt conveys the recording paper P and the toner image is transferred from each photosensitive drum 121 to the recording paper P is also an embodiment of the present invention. In this case, the transfer of the toner image to the intermediate transfer belt by the transfer roller in the claims means the transfer of the toner image to the intermediate transfer belt by the transfer roller.

  In the above embodiment, the cleaning member 531 is formed of a conductive material, but the material of the cleaning member 531 is not limited to a conductive material.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. The configurations and processes shown in the above embodiments using FIGS. 1 to 6 are only one embodiment of the present invention, and the configurations and processes of the present invention are not limited thereto.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 12 Image forming part 12Bk Image forming unit 12C Image forming unit 12M Image forming unit 12Y Image forming unit 121 Photosensitive drum 122 Developing device 123 Charging device 124 Exposure device 125 Intermediate transfer belt 126 Primary transfer roller 50 Intermediate transfer unit 51 Frame 52 Drive Mechanism 521 First Rotating Shaft 522 First Support Member 522a First Locking Part 524 Rotation Driving Part 525 Engaging Part 525a First Engaging Part 525b Second Engaging Part 53 Cleaning Unit 530 Moving Mechanism 531 Cleaning Member 532 2nd rotating shaft 533 2nd support member 533a 2nd latching | locking part 5331 Recessed part 125a Drive roller 125b Followed roller

Claims (5)

A toner image formed by an image carrier of each color necessary for color and monochrome image formation is transferred to a surface or transferred to a recording medium placed on the surface while being stretched between a plurality of rollers. A transfer belt
A transfer roller that is provided for each image carrier, applies a transfer potential to the transfer belt, and transfers the toner image to the transfer belt;
Among the transfer rollers for color and monochrome image formation, a drive mechanism for contacting and separating the transfer rollers for color image formation with respect to the transfer belt;
A cleaning member capable of contacting the back surface of the transfer belt, and cleaning the back surface;
When the drive mechanism moves the transfer rollers for forming the color image to a position in contact with the transfer belt, the drive mechanism moves the cleaning member to a position in contact with the back surface of the transfer belt, and the drive mechanism A transfer unit that moves the cleaning member to a position away from the back surface of the transfer belt when each of the transfer rollers for forming the color image is moved to a position away from the transfer belt. . The drive mechanism supports the first rotation shaft in a state where the first rotation shaft extending in the rotation axis direction of the roller and the transfer rollers for forming the color image arranged in the running direction of the transfer belt are supported. A first support member that rotates as described above and rotates the transfer rollers for forming the color image in a direction in contact with and away from the back surface of the transfer belt, and a rotation drive unit that rotationally drives the first support member. Prepared,
The moving mechanism includes: a second rotating shaft extending in a rotating shaft direction of the roller; and a second supporting member that rotates about the second rotating shaft while supporting the cleaning member. For the position opposite to the position where each transfer roller for forming the color image is disposed,
In the first support member, a first locking portion provided closer to the movement mechanism than the first rotation shaft, and in the second support member, a first engagement portion provided closer to the drive mechanism than the second rotation shaft. And when the first support member rotates the transfer rollers for forming the color image away from the back surface of the transfer belt, the first engagement member is engaged with the first engagement member. 2. The transfer unit according to claim 1, wherein the stop portion presses the second locking portion to rotate the second support member in a direction in which the cleaning member is separated from the back surface with the second rotation shaft as a fulcrum.   The transfer unit according to claim 1, wherein the cleaning member is in contact with the back surface in a state where the back surface of the transfer belt is pressed.   The transfer unit according to claim 1, wherein the cleaning member is formed of a conductive material. The image carrier;
A charging unit for charging the peripheral surface of the image carrier;
An exposure unit that exposes the peripheral surface charged by the charging unit;
A developing unit that applies toner to the electrostatic latent image generated on the peripheral surface by exposure by the exposure unit and develops the toner;
The transfer unit according to any one of claims 1 to 4,
An image forming apparatus comprising: a second transfer unit that transfers a toner image on the transfer belt to a recording medium.

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